earth talk 2-17-05

Dear “Earth Talk”: What has been causing
holes in the Earth’s ozone layer, and what is being done about it?
— Marcin Wasilewski, Delray Beach, Fla.

Chemicals called chlorofluorocarbons (CFCs), of which
there are many variations, are the prime culprits in the depletion of the
Earth’s ozone layer. The ozone layer is composed of ozone molecules,
which bind together in the Earth’s stratosphere to serve as
Earth’s sunglasses, shielding us from damaging ultraviolet rays.
Meanwhile, CFCs, commonly used in refrigerants and aerosol sprays, are
virtually indestructible and linger in the atmosphere, destroying ozone
molecules faster than they can regenerate.

The problem is most acute over Antarctica, where, in
2004, an area of more than 9 million square miles — two-and-a-half
times the area of Europe — was affected. Australia, North America,
and Europe are also at great risk from ozone depletion. Greater exposure to
ultraviolet light resulting from a thinning ozone layer leads to an
increased incidence of skin cancers and eye cataracts, as well as lessened
disease immunity. Ozone depletion also causes damage to ocean ecosystems
and reduces agricultural yields, and it may be affecting the reproductive
abilities of some amphibians, especially frogs, whose populations are
falling rapidly around the globe.

In 1987, 24 countries signed the Montreal Protocol, an
agreement to reduce CFC production worldwide through a phase-out of 96
different chemicals. CFC production is now banned in most countries, and
use began to decline after peaking in 2000. According to the United Nations
Environment Programme, which oversees implementation of the Montreal
Protocol, the ozone layer should be able to repair itself by 2050 as long
as CFC production trails off as planned.

Despite widespread ratification and implementation of
the Montreal Protocol, some environmental groups do not think enough is
being done to protect the ozone layer. For one, black-market trading in
CFCs is a big problem that perpetuates the discharge of these chemicals
into the atmosphere. And a growing number of scientists are concerned that
newer, increasingly popular chemicals such as n-propyl bromide and
halon-1202, neither of which is controlled by the Montreal Protocol, could
contribute significantly to ozone depletion. n-Propyl bromide is used
primarily as a degreasing solvent in metal cleaning, and halon-1202 is used
in military firefighting equipment. In fact, the presence of halon-1202 in
the atmosphere has increased fivefold since the late 1970s.

“At the moment I believe we do not have a big
problem with these new substances,” says Massachusetts Institute of
Technology professor Mario Molina, who is credited with discovering the
problem of ozone depletion caused by CFCs in the 1970s, “but we
cannot be complacent. If enough of them are manufactured and emitted, we
will delay the recovery of the ozone layer quite significantly.”

“Early recovery is possible with an aggressive
commitment,” agrees Beatrice Olivastri, CEO of Friends of the Earth
Canada. “Governments need to stop rolling back legislation for a
total ban on these chemicals.”